Dyes are used as tracers to detect leaks within fluid systems. Fluid systems are closed systems that include a fluid, either gas or liquid. Fluid systems include, for example, refrigerant systems, transmission systems and hydraulic systems.
One of the most effective methods for detecting leaks in refrigeration systems, and a preferred method to be practiced with the present invention, comprises introducing into a refrigeration system an effective amount of a fluorescent dye compound. The dye compound circulates with the refrigerant and system lubricating oil throughout the refrigeration circuit, and is carried out with escaping refrigerant and oil at a leak site. When the refrigeration system is exposed to ultraviolet light, even a small deposit of the dye compound is brilliantly fluorescent to allow visual detection of the leak. U.S. Pat. No. 5,149,453 discloses such a method for detecting leaks in a refrigeration system, and its entire content is incorporated herein by reference.
U.S. Pat. No. 5,650,563, reissued as U.S. Pat. No. Re. 36,951, the entire disclosure of which is incorporated herein by reference, describes placing a dye into a closed air conditioning or refrigeration system prior to the initial refrigerant charging of the system. Re. 36,951 describes saturating an absorbent wafer, or other suitable substrate carrier, with a mixture of a dye and a solvent for the dye, such as a refrigerant system lubricating oil. This system of placing dye on the substrate carrier is sometimes known as a “wet” system because the dye remains in a liquid state.
It is also known to place a leak detection dye onto a wafer by saturating the wafer with a mixture of dye powder and alcohol. Following evaporation of the alcohol, the dye remains in the form of dye solids dispersed through the wafer. This system of placing dye onto a carrier wafer is sometimes referred to as a “dry” system because of the evaporation of the alcohol from the saturating mixture leaves a dye impregnated wafer. Dye carrier wafers are described in U.S. Pat. No. 5,650,563, reissued as U.S. Pat. No. Re. 36,951, and in U.S. Pat. No. 7,552,623, the entire disclosure of which is incorporated herein by reference.
The dye carrier wafer for use in a refrigerant system is made from a substrate material that is absorbent to liquid but does not react with the refrigerant or system lubricant circulated through a closed refrigeration system. A preferred wafer material is made from a melamine-treated polyester felt mat. The wafer carries a leak detection dye that will be released into the refrigeration system from the wafer when the system is charged with a circulating refrigerant. Thus the dye carrier wafer may be placed within the closed refrigeration system circulated before the system is charged with refrigerant, thus avoiding the need to insert liquid dye into a system already charged with refrigerant. For use in automotive air conditioning systems, the dye carrier wafer must be capable of releasing a detectable portion of its dye within a short period after the system's charging with refrigerant, as leak detection is routinely carried out after charging.
After releasing its dye, the dye carrying wafer, or other inert substrate onto which the dye is absorbed, will remain in the closed air conditioning or refrigeration system, and will longer serve any purpose. Moreover, the impregnation of the dye onto a substrate material requires additional steps, materials and expense in dye product formulation. What is needed is an alternative dye composition that provides the advantages of a substrate-based dye carrier for use in leak detection in fluid system, particularly refrigeration systems.